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My Tone Pots have suddenly stopped working-help!

Deepmojoman

New member
Joined
May 4, 2020
Messages
5
I am STUMPED! Completely FLUMMOXED! I've reached the end of my solutions, and I need you guys' help.

I've had this Epi Les Paul-a 2013 model-since '15. Soon after purchasing it I replaced the sucky Push-Pull pots-the ones with the Molex connector; the ones whose stems often pull out-with the better Push Push models, and I have been happy with those for years.

For the past few months one or the other of the tone pots would just stop working. I'd open up the electronics compartment, jiggle a few wires and the pot would come back to life. So I knew that I had some imperfect wiring going on that I'd eventually have to get around to fixing.

Then last Monday I noticed that, once again, one of the tone pots had gone south. I opened up the compartment and found this time that jiggling wires didn't work. So I figured that whatever shorts in the wiring that I knew would eventually come to stay had, in fact, done just that, so I got out my gear and went to work.

To cut to the chase: NONE of it brought my tone pots back.

Here is a list of all the things I did:

1. I ended up replacing ALL the wiring-the set of wires coming from the pickup selector, as well as both sets of wires coming from both Pickups-twice. First I replaced the wiring with 18 ga solid wiring, and then later thought that the stiffness of the solid wiring was helping to pry soldered joints free on the replacement pots, so then I ended up replacing all the solid wire with more flexible stranded wire.

2. Both Push-Push pots have been completely replaced.

3. Both Tone Pots and their Caps have been completely checked and are working properly and to spec.

4. New Tone Pots were installed, along with new Caps, just to see if the problem was somehow the Tone Pots (even though, as mentioned before, all Pots/Caps checked out fine.) Installing the new Pots/Caps changed nothing.

5. All grounds have been continuity checked and are fine. Bridge to Neck Tone Pot, as per the included schematic.

6. Continuity tests have been run between the P/U Selector and the Electronics compartment, and all wires pass with flying colors.

7. The Pickups have been removed from their recesses and looked at for any signs of any abnormality. They are the stock Epiphone-designed models, and are sealed, and both look completely normal.

8. Through progressively rewiring more and more of the compartment, I have gotten the electroncs buttoned down better than perhaps they have ever been. No more "Jiggle Shorts" anywhere. And the tone seems to have gotten better (no surprise). Just: no ability to modulate the tone with the Tone Knobs.

So that's my story. The pic I am including is the schematic of the wiring. My wiring exactly matches the schematic.

How the Tone Pot modulates your tone is a fairly simple electronic affair, right? Signal comes into the Volume Pot via the red wire from either pickup, and is soldered to the leftmost lug. That lug is shared by a wire coming from the Tone Pot and-regardless of what wiring scheme you've chosen to wire your Tone Pots (from '50s, to Modern, and any mode in between,)-the high frequencies of the signal in the Volume Pot will be attenuated by the Cap attached to the Tone Pot, before exiting the Volume Pot via the middle lug.

As long as the Tone Pot is attenuating signal (which it is, in a constant sweep, from 0 to 500K ohms, as it should,) and the Cap is to spec (which it is: .022 uf), and there is a clear path for the attenuated high frequencies to escape to via a clear Ground (which there is), then this should work. And yet it doesn't

So does anyone have any insights?? I am completely stumped.

https://drive.google.com/open?id=1FilmmaP9E6iw189fpAH1m85LUsyK5WAb
 

au_rick

Active member
Joined
Mar 18, 2010
Messages
871
I am STUMPED! Completely FLUMMOXED! I've reached the end of my solutions, and I need you guys' help.

I've had this Epi Les Paul-a 2013 model-since '15. Soon after purchasing it I replaced the sucky Push-Pull pots-the ones with the Molex connector; the ones whose stems often pull out-with the better Push Push models, and I have been happy with those for years.

For the past few months one or the other of the tone pots would just stop working. I'd open up the electronics compartment, jiggle a few wires and the pot would come back to life. So I knew that I had some imperfect wiring going on that I'd eventually have to get around to fixing.

Then last Monday I noticed that, once again, one of the tone pots had gone south. I opened up the compartment and found this time that jiggling wires didn't work. So I figured that whatever shorts in the wiring that I knew would eventually come to stay had, in fact, done just that, so I got out my gear and went to work.

To cut to the chase: NONE of it brought my tone pots back.

Here is a list of all the things I did:

1. I ended up replacing ALL the wiring-the set of wires coming from the pickup selector, as well as both sets of wires coming from both Pickups-twice. First I replaced the wiring with 18 ga solid wiring, and then later thought that the stiffness of the solid wiring was helping to pry soldered joints free on the replacement pots, so then I ended up replacing all the solid wire with more flexible stranded wire.

2. Both Push-Push pots have been completely replaced.

3. Both Tone Pots and their Caps have been completely checked and are working properly and to spec.

4. New Tone Pots were installed, along with new Caps, just to see if the problem was somehow the Tone Pots (even though, as mentioned before, all Pots/Caps checked out fine.) Installing the new Pots/Caps changed nothing.

5. All grounds have been continuity checked and are fine. Bridge to Neck Tone Pot, as per the included schematic.

6. Continuity tests have been run between the P/U Selector and the Electronics compartment, and all wires pass with flying colors.

7. The Pickups have been removed from their recesses and looked at for any signs of any abnormality. They are the stock Epiphone-designed models, and are sealed, and both look completely normal.

8. Through progressively rewiring more and more of the compartment, I have gotten the electroncs buttoned down better than perhaps they have ever been. No more "Jiggle Shorts" anywhere. And the tone seems to have gotten better (no surprise). Just: no ability to modulate the tone with the Tone Knobs.

So that's my story. The pic I am including is the schematic of the wiring. My wiring exactly matches the schematic.

How the Tone Pot modulates your tone is a fairly simple electronic affair, right? Signal comes into the Volume Pot via the red wire from either pickup, and is soldered to the leftmost lug. That lug is shared by a wire coming from the Tone Pot and-regardless of what wiring scheme you've chosen to wire your Tone Pots (from '50s, to Modern, and any mode in between,)-the high frequencies of the signal in the Volume Pot will be attenuated by the Cap attached to the Tone Pot, before exiting the Volume Pot via the middle lug.

As long as the Tone Pot is attenuating signal (which it is, in a constant sweep, from 0 to 500K ohms, as it should,) and the Cap is to spec (which it is: .022 uf), and there is a clear path for the attenuated high frequencies to escape to via a clear Ground (which there is), then this should work. And yet it doesn't

So does anyone have any insights?? I am completely stumped.

https://drive.google.com/open?id=1FilmmaP9E6iw189fpAH1m85LUsyK5WAb


Maybe remove one of the earth wires so you do not have an earthing loop ?
 

PaulD

Active member
Joined
Jun 25, 2007
Messages
673
You cannot have an "earthing loop" in guitar wiring, a ground loop is when two parts of a circuit that should be at ground potential are at different potentials, this results in current flowing between the two points which can result in hum in an audio circuit. The only current in a guitar is that generated by the pick ups and ground loops are not applicable in this context.

To the OP, your understanding of the tone control circuit is correct, it is a simple treble bleed circuit with the tone pot wired as a variable resistor. Turning the tone control down reduces the resistance and allows more of the high frequency part of the signal to bleed to ground through the capacitor (the value of the capacitor determines the roll off frequency). You seem to have checked most things but clearly there is something not right, I would suggest a double check of all parts of the tone circuit, check for continuity between the volume pot connection to the tone pot connection and from the back of the tone pots to the sleeve of the output jack. If all of the connections are good then the only other things that could be causing it is faulty pots or faulty capacitors. One thing you could try is bypassing the capacitor by temporarily shorting between the centre lug and the back of the tone pot (a clip lead or just shorting with a screwdriver should do it). With this done the tone control should now act as a volume control, if it doesn't the problem is either a faulty pot or a bad connection, if it does work as volume control then the capacitor is faulty.
 

Deepmojoman

New member
Joined
May 4, 2020
Messages
5
Thanks for the insights Paul. I haven't yet tried out your Pot/Cap test but I will soon and give an update. Nonetheless I wanted to share a thought I had last night and see if cuts the mustard with anyone.

I was in the studio working on some preamps-specifically, I was tweaking the impedance settings. I was taking note of how dark the tones of the vocals were whenever I would turn the impedance down. So I had a thought: is there somehow something here that is relevant to my Les Paul electronics?

So, if I'm not mistaken (and if I am, my apologies: I'm still trying to get my head fully around the concept of impedance) perhaps the way in which my experience with my preamp might be relevant to my LP tone electronics is: the less impedance (impedance being resistance/capacitance of certain frequencies)) the High Frequencies experience as they attempt to return to ground, the easier it will be for them to do just that. Therefore, when your lowering your impedance in a tone circuit, you're making an easier, clearer path for those HF to leak from the signal, and the signal gets "darker". Does that sound right?

Well, I'm not yet fully clear on how all this works in a Tone circuit, as you can see, all I know is once I started messing around with impedance settings of difference preamps and noticing how they all behave in the same low impedance=darker tone sort of way made me think that somehow impedance/resistance/wiring in the Electronics Compartment might have a big part in all this.

It's all just completely deductive "connect the dots" kind of reasoning here at this point. All I know is this: the only thing in my Electronics Compartment that has completely changed has been The Wiring. The wiring has changed in two ways:

1. 90% of the new wires are now of a larger gauge (I know: which would seem to suggest less resistance/impedance. Confusing) than what was in the compartment when it had been working for years.

2. ALL of the ground wires are now not only of a larger gauge but are solid, with some sort of silvery coating (Steel? Tin?) and with a copper core. I didn't know that some people recommend to "nick" this type of wire before using it in any type of install like this-assumedly to aid in current passage.

Some of the stock wiring in the Electronics compartment looks to be, maybe as small as 24-26 ga. If there did exist such a wide differential in gauge size, is there a possibility that this, somehow, has taken the electronics out of the range of impedance needed for the Tone circuit to operate properly?


BTW: right before I turned in last night, I decided I would replace the caps that were installed with new caps of different specs. When I did so: it worked. The Tone circuit DID respond, starting to attenuate HF in the way that tone circuits do-with one difference: all the attenuation occurred within the first few fractions of travel of the pot. It was as if the first 1/8" of the potentiometer graphite band moved in resistance from 500K to 75K, with the entire remaining portion of the pot going from 74K to 0K. So that did strongly suggest something: the source of my problems does lie, somehow, in the area of the Pot. Whether it's because the pot can't send out HF in the way it wants to, because of impedance, or because the pot needs replacement, or because it no longer wants/likes .022 uf caps-for whatever reason, in trying to figure out this riddle, this moment taught me to look closer at the Pots.

But: why would a Tone circuit that had been working perfectly for years with .022 uf caps, all of sudden no longer work with them, and only work with a different cap value (.068 uf)?

Sorry for the ramble. I'm not operating on a lot of sleep here. Thanks for the help.
 

PaulD

Active member
Joined
Jun 25, 2007
Messages
673
You are over complicating things a bit. Impedance can be a confusing and complicated subject but in simple terms it is resistance to the passage of AC current. Some components are non reactive and will exhibit the same resistance to AC current as they do to DC current: resistors and pots fall into this category. Other components are reactive and their resistance to current flow will depend upon the frequency of the AC waveform: capacitors, coils and inductors are all examples of reactive components. In the case of the guitar tone control the simplest way to understand it is to think of the tone pot as a tap or valve, when it is turned up to 10 the tap is closed, nothing passes through it and all of the signal goes to the output jack. As you turn the control down you are progressively opening the tap to allow more current to flow through it and bleed off to ground but because it has a capacitor in series with it the capacitor will only allow the high frequencies to pass through, the capacitor being a reactive component will have a high resistance to the lower frequencies but a much lower resistance to the higher frequencies.

As for the gauge of wire used in the guitar, this will have no effect whatsoever. The resistance of the short pieces of wire inside the guitar will be measured in micro ohms and any differences due to the gauge of wire used would miniscule and irrelevant.

The tone control behaviour you describe sounds like it has linear taper pots as opposed to log taper. When linear pots are used as tone controls they can often behave more like an on/off switch than a tone control! It seems strange that you say this only occurred after changing the caps though so not really sure about that. The only thing I can think of is that using a higher value cap will mean that more frequencies will be being rolled off so maybe it has just made the effect more noticeable than before?
 

Deepmojoman

New member
Joined
May 4, 2020
Messages
5
Well, after looking at the wiring with a much clearer (i.e.: well-rested) head I'm pretty sure I've figured out what's going on:

thejaf: "Was the pot damaged by heat from solder iron?"

Yes, it looks like constant unsoldering/resoldering of the exit lug on both my tone pots has developed a short in both of them. When I temporarily grafted another 500K pot into the mix, connected various caps into the circuit they were all modulating the tone. Thus it is clear that what I need are new pots, so I have ordered a pair of 500K Audio taper pots from StewMac.

I figured out what you figured out, Paul, which is that the reason for the weird abrupt tone change was mostly because of a linear pot. The pot that I temporarily grafted into the circuit (stem not long enough to mount permanently) was an Audio Taper, and it sounded much better.

It is strange that this guitar, with the original caps on the tone pots always sounded to me like they should, and then all of a sudden, with the same setup, it sounds/behaves so differently. It's definitely possible that there's some psychoacoustic favoring going on with me, seeing as I've been "staring" at the performance of the Tone circuit for a week now. Maybe, under such a microscope as this, my ears have become more sensitive to something it only noticed in passing. Who knows?

All I know is it was good to finally figure out such a bothering mystery. If the pots get here, and things still aren't fixed, I'll sure let you know. But thanks for the help you've all given.
 

corpse

Well-known member
Joined
Jun 9, 2007
Messages
4,876
Some a couple things- and don't take this as any sort of insult please.
1) Make sure the pot is set at zero (which I do now) or full on 10 when you solder. It keeps the "innards" from being exposed to heat.
2) Pre-tin all the parts (with flux of course) and then you only need to apply minimal heat to flow the solder. Trying to apply solder to two components seems to take a lot longer and could be part of the issue.
 

Deepmojoman

New member
Joined
May 4, 2020
Messages
5
Some a couple things- and don't take this as any sort of insult please.
1) Make sure the pot is set at zero (which I do now) or full on 10 when you solder. It keeps the "innards" from being exposed to heat.
2) Pre-tin all the parts (with flux of course) and then you only need to apply minimal heat to flow the solder. Trying to apply solder to two components seems to take a lot longer and could be part of the issue.

Both really good bits of advice, although admittedly, I've never heard of the setting the pot at zero thing before. Seems to make sense though-thanks. I do pre-tin btw: it does make things WAAY easier, as you're atesting to.
 

corpse

Well-known member
Joined
Jun 9, 2007
Messages
4,876
DMM
Sounds like it is fixed.
As a funny side note- I don't think I ever took my tone pots off of 10- ever- for decades- until I started coming to the LPF 15 years ago. Maybe fora woman-tone thing but that was it.
 

Deepmojoman

New member
Joined
May 4, 2020
Messages
5
Embarrassing (and yet educational) update!!

Well . . . after going through one week of Les Paul hell-complete with re-doing the wiring, installing a new set of Push-Push pots and-most notably-installing two new capacitors with completely new values onto the Tone pots-after all that I figured out that NONE of these were the reason why I was not getting any tone modulation from my Tone pots.

The REAL culprit was: (drumroll): a bad cable.

I had put together a homemade cord with Livewire cable and Neutrix connectors on both ends. And one of the ends somehow had a short in it. In using True RTA to pass a 1000 Hz Sine wave at 0 dbu through any well functioning cable, my Multimeter reads .188mv. Doing that with the faulty cable the Multimeter was reading .164 mv. It might not seem like much but, you must trust me: that was A LOT of signal loss. I know this because after switching the faulty cabling out for a good cable, the guitar that now has higher cap values in it (stock it came with .22uf, and in order to get a satisfying tone modulation with what turned out to be this faulty cable, I had to use .063 uf caps) dumps almost ALL highs out of the signal with the knob bottomed out! An interesting sound.

So, anyway, I just finished replacing the bad Neutrix connector with another, did Sine tests, and when everything checked out, I reconnected it to my guitar. All is as it was before: except I will probably eventually take those .063 uf caps and put back in the stock .022s. But-who knows: maybe I'll keep them in as an interesting effect. Haven't fully decided.

So, to all out there who might be struggling for an answer to why your guitar, in any way, is starting to sound a little different, don't knock the concept of first trying the obvious: suspecting the cable first. Trust me: it can make an ASTOUNDINGLY large difference.

Thanks for reading. Stay safe.
 
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